The effect of coastal processes on phytoplankton biomass and primary production within the near-shore Subtropical Frontal Zone

• Published in: Estuarine, Coastal and Shelf Science
• Main Authors: Jones, KN, Currie, KI, McGraw, CM, Hunter, KA
• Format: Article in Journal/Newspaper
• Language: English
• Published: Academic Press Ltd Elsevier Science Ltd 2013
• Subjects: Earth Sciences; Oceanography; Biological Oceanography; Antarctic; Austral; Antarc*
• Online Access: https://doi.org/10.1016/j.ecss.2013.03.003; http://ecite.utas.edu.au/89582

This study evaluated drivers of phytoplankton net primary production (NPP) rates and chlorophyll-a (chla)concentrations within the coastally oriented Subtropical Frontal Zone (STFZ) off the South Island ofNew Zealand. Time series measurements of hydrographic parameters, macronutrients, size fractionatedNPP and chl-a were conducted on a bi-monthly basis from July 2009 to November 2010. This study foundthat nutrient limitation in these waters is controlled by the dual influx of silicate inputs from riverinesources in coastal neritic water (NW) and oceanic inputs of nitrate from the high nutrient, low chlorophyll(HNLC) region of the offshore Sub-Antarctic Surface Waters (SASW). Total chl-a concentrations andprimary production rates were perennially higher in near-shore NW and modified Subtropical waters(STW) than in the SASW, with highest indicators of biological production observed in the Austral springand summer seasons (October to March). These periods of peak production and biomass were dominatedin both parameters by microphytoplankton (>20 mm) size fractions. The coupled dominance by theselarge phytoplankton and the near depletion of silicate in all characterised waters within the frontalsystem indicate the importance of silicic diatoms as drivers of bloom production. The influence of coastalwaters on the STFZ system is most pronounced with the intrusion of neritic water beyond the shelfboundary during periods of surface water thermal stratification and riverine dilution through floodingevents. These two events were notably observed during the Spring 2009 sampling cruise in December2009 and in the flood event in May 2010.